Yasuyuki Takai

The role of tumor-specific Lyt-1+2− T cells in eradicating tumor cells in vivo

SummaryThe present study investigates some of mechanisms for tumor-specific Lyt-1+2− T cell-mediated tumor cell eradication in vivo through analyses of tumor specificity in the afferent tumor recognition and efferent rejection phases. When C3H/He mice which had acquired immunity against syngeneic MH134 hepatoma were challenged with other syngeneic X5563 plasmacytoma cells, these mice failed to exhibit any inhibitory effect on the growth of X5563 tumor cells. However, the inoculation of X5563 tumor cells into the MH134-immune C3H/He mice together with the MH134 tumor cells resulted in appreciable growth inhibition of antigenically distinct (bystander) X5563 tumor cells. Although the growth of X5563 cells was inhibited in an antigen-nonspecific way in mice immunized to antigenically unrelated tumor cells (bystander effect), the activation of Lyt-1+2− T cells leading to this effect was strictly antigen-specific. Such a bystander growth inhibition also required the admixed inoculation of the bystander (X5563) and specific target (MH134) tumor cells into a single site in mice immunized against the relevant MH134 tumor cells. Furthermore, the results demonstrated that Lyt-1+2− T cells specific to MH134 tumor cells were responsible for mediating the growth inhibition of antigenically irrelevant (bystander) and relevant tumor cells. These results are discussed in the context of cellular and molecular mechanisms involved in the Lyt-1+2− T cell-initiated bystander phenomenon.

Capacities of a Newly Established Thymic Stromal Cell Clone to Express Ia Antigens and to Produce Interleukin-6, Colony-Stimulating Factor, and Thymic Stroma-Derived T-Cell Growth Factor

Thymic stromal cell lines, termed MRL104 and MRL28, have been isolated from long‐term liquid cultures of thymic stromal cells from MRL/1 mice. The capacities of these parental lines and derived clones to express la antigens and to produce cytokines involved in T‐cell proliferation and/or differentiation were investigated. Parental lines and their clones did not exhibit a typical fibroblastic, macrophage‐like, or epithelial appearance in electron as well as phase‐contrast micrographs. These thymic stromal cells seemed to differ from established fibroblast lines in that these thymic stromal cells expressed la antigens after exposure to interferon‐γ (IFN‐γ), whereas fibroblast lines did not They also appeared to differ from macrophage cell lines in that they lacked the expression of Mac‐1 antigens on their cell surface and produced no detectable level of interteukin‐1 (IL1) before or even after exposure to lipopolysaccharide. When these parental lines and its clones were tested for their ability to produce various types of cytokines, it was revealed that they were capable of producing colony‐stimulating factor (CSF), IL6, and thymic stroma‐derived T cell growth factor (TSTGF). which was recently described, but were unable to generate other lymphokines and IFNs. Thus these cell lines and clones represent unique features in that they have potentials to express la antigens and to produce CSF, IL6, and TSTGF. The biological significance for the expression of these features is discussed in the context of intrathymic T‐cell maturation and T‐cell repertoire selection.

The augmentation of tumor-specific immunity by virus help. III. Enhanced generation of tumor-specific Lyt-1+2- T cells is responsible for augmented tumor immunity in vivo.

The role of vaccinia virus-reactive helper T cells (Th) in augmenting in vivo generation of antitumor protective immunity and the Ly phenotype mediating the enhanced in vivo tumor immunity were investigated. C3H/HeN mice were inoculated i.p. with viable vaccinia virus to generate vaccinia virus-reactive Th activity. The mice were subsequently immunized i.p. with virus-infected syngeneic X5563 and MH134 tumor cells, and spleen cells from these mice were tested for in vivo tumor neutralizing activity. Immunization of virus-primed mice with virus-uninfected tumor cells and of virus-unprimed mice with virus-infected tumor cells failed to result in in vivo protective immunity. In contrast, spleen cells from mice immunized with virus-infected tumor cells subsequent to virus-priming exhibited potent tumor-specific neutralizing activities. Such an augmented generation of in vivo protective immunity was accompanied by enhanced induction of tumor-specific cytotoxic T lymphocyte (CTL) and antibody activities in X5563 and MH134 tumor systems, respectively. However, analysis of the effector cell type responsible for in vivo tumor neutralization revealed that enhanced in vivo immunity was mediated by Lyt-1+2- T cells in both tumor systems. Moreover, the Lyt-1+2- T cells exerted their function in vivo under conditions in which anti-X5563 tumor-specific CTL or anti-MH134 tumor-specific antibody activity was not detected in recipient mice. These results indicate that augmenting the generation of a tumor-specific Lyt-1+2- T cell population is essential for enhanced tumor-specific immunity in vivo.

The augmentation of tumor-specific immunity by virus help

SummaryThe role of vaccinia virus-reactive helper T cells (Th) in augmenting in vivo generation of antitumor protective immunity and the Ly phenotype mediating the enhanced in vivo tumor immunity were investigated. C3H/HeN mice were inoculated i.p. with viable vaccinia virus to generate vaccinia virus-reactive Th activity. The mice were subsequently immunized i.p. with virus-infected syngeneic X5563 and MH134 tumor cells, and spleen cells from these mice were tested for in vivo tumor neutralizing activity. Immunization of virus-primed mice with virus-uninfected tumor cells and of virus-unprimed mice with virus-infected tumor cells failed to result in in vivo protective immunity. In contrast, spleen cells from mice immunized with virus-infected tumor cells subsequent to virus-priming exhibited potent tumor-specific neutralizing activities. Such an augmented generation of in vivo protective immunity was accompanied by enhanced induction of tumor-specific cytotoxic T lymphocyte (CTL) and antibody activities in X5563 and MH134 tumor systems, respectively. However, analysis of the effector cell type responsible for in vivo tumor neutralization revealed that enhanced in vivo immunity was mediated by Lyt-1+2− T cells in both tumor systems. Moreover, the Lyt-1+2− T cells exerted their function in vivo under conditions in which anti-X5563 tumor-specific CTL or anti-MH134 tumor-specific antibody activity was not detected in recipient mice. These results indicate that augmenting the generation of a tumor-specific Lyt-1+2− T cell population is essential for enhanced tumor-specific immunity in vivo.

T-T cell interaction in the in vitro induction of delayed-type hypersensitivity (DTH) responses: demonstration of vaccinia virus-reactive helper T cell activity involved in enhanced induction of DTH responses.

C3H/HeN mice were inoculated i.p. with viable vaccinia virus to generate virus‐ reactive helper T cell activity. 850R X‐irradiated spleen cells from vaccinia virus‐primed or unprimed mice as helper cells were stimulated in vitro with either trinitrophenyl (TNP)‐modified syngeneic spleen cells (TNP‐self), vaccinia virus‐infected spleen cells (virus‐self), or cells modified with TNP subsequent to virus infection (virus‐self‐TNP) in the presence of normal C3H/HeN spleen cells (responding cells). After 5 days of culture, effector cells were tested for anti‐TNP delayed‐type hypersensitivity (DTH) responses by adoptive transfer into footpads of syngeneic C3H/HeN recipient mice together with TNP‐self. The results demonstrate that spleen cells from virus‐primed mice failed to enhance anti‐TNP DTH responses when in vitro stimulation was provided by either virus‐self or TNP‐self alone. In contrast, spleen cells from vaccinia virus‐ primed mice, but not from unprimed mice, could augment anti‐TNP DTH responses when stimulated by virus‐self‐TNP. Such a helper activity provided by vaccinia virus‐primed mice was shown to be antigen‐specific, and mediated by Lyt‐1+2−T cells. DTH effector cells enhanced by helper cells were also antigen‐specific and Lyt‐1 +2−T cells. Furthermore, vaccinia virus‐reactive helper T cell activity could be applied to augmented induction of anti‐tumor DTH responses by stimulation with virus‐infected syngeneic fibrosarcoma tumor cells. Thus, these results provide evidence for the role of antigen‐specific helper T cells in augmenting the development of DTH responses to cell surface antigens including tumor antigens.

Application of T Cell—T Cell Interaction to Enhanced Tumor-Specific Immunity Capable of Eradicating Tumor Cells in Vivo

Investigations have attempted to delineate the consequences of malignant transformation of cells by the appearance of new cell surface structures [tumor-associated antigens (TAA) or tumor-associated transplantation antigens (TATA)] that could be identified by specific antiserum or by their ability to induce a specific cellular immune response. Considerable efforts have been undertaken to establish the significance of these tumor cell surface structures by correlating their cell surface expression with changes that take place during the course of neoplastic disease. The most compelling evidence for the existence of TATA comes from the study of chemically induced tumors of inbred rodents. These tumors express neoantigens capable of immunizing syngeneic or autochthonous hosts against subsequent challenge with the same tumor.(1–4)